In maritime Simultaneous Operations (SIMOPS), efficient and secure communication between the involved parties is of vital importance. The communication systems in use today is mainly standard VHF and satellite communication which needs to be coordinated between the parties before the operation. VHF communication is a proven method of speech communication, but does not support the high data rates that is necessary in complex operation involving DP systems, electronic chart systems (ECS, ECDIS) and computer controlled decision support systems. Satellite communication may support high data rates, but it often introduces unwanted delays in the communication chain. Today's complex SIMOPS therefore require a long range, high speed data communication system tailored to integrate a large number of data communication sources and supporting live video from the entities involved.
Off the shelf broadband networks are not well suited for SIMOPS environments due to short range and low resistance to interference. The capacity of such networks is also too low to support the demanding applications found in SIMOPS. Moreover, such units are not optimized for transmission over sea which may heavily degrade their performance.
GB2448510 A discloses a radio frequency communication method, apparatus or system which comprises a first antenna which transmits information regarding its location to a second antenna which receives the said information and uses it to align a directional radiation beam from the second antenna towards the location of the first antenna. The publication describes a lobe-aligning system based on switching antennas between omnidirectional antennas transmitting location information and highly directive antennas which are used for communication purposes. Even if alignment is achieved, the dual antenna approach is complex and expensive. The use of omnidirectional antennas will also limit the system range as they have zero antenna gain. Even if transmission speed is lowered to overcome this problem, this system will never perform as good as a system with high antenna gain for both location and data transmission.
US2005176372A discloses a highly integrated reliable architectural radio system for maritime application. Especially, US2005176372A relates to a wireless unlicensed band radio system for use in maritime applications which comprise three sector antennas providing a minimum of 120 degrees coverage (3 dB point) which combine to achieve 360 degrees of continuous coverage. The publication describes the use of standard WLAN equipment in a configuration where separate units are used for covering separate sectors. Standard WLAN equipment is not well suited for use over open sea paths where sea reflections will contribute to deep nulls, low signal to noise ratio and inter-system interference problems. Moreover, standard WLAN equipment has reduced capacity when several users are logged on the network. As reflections and interference signals are to be expected in marine environments, the standard WLAN approach will normally not meet the demanding requirements in SIMOPS.
US2002169527 discloses a method and system for a marine vessel tracking system. Especially, US2002169527 relates to automatic marine ship tracking systems and methods. More particularly, this disclosure relates to ship tracking systems and methods for accurately monitoring the movement of marine ships utilizing a limited number of transmissions from the marine ships. The publication describes a simple tracking system based on GPS and wireless transmission of position data to a central control unit. The vessels only report when a major shift in position from the last report is observed. The control unit extrapolates the position data and can pinpoint the position of the vessel with some accuracy. The described system is not sufficient for the position data rate needed in SIMOPS. As SIMOPS is characterized by vessels and structures close to each other, the position update must be close to real time. Data capacity and speed is therefore highly important. SIMOPS communications must in addition be virtual, as will be described in the present application.
US2006276992 describes a segmented antenna system for offshore radio networks and a method of using the same. Especially, US2006276992 relates to a radio network, and more particularly, to a segmented antenna system for an offshore radio network used in marine seismic surveying. The publication describes antenna lobe steering by switching physical antennas arranged in a circle in order to obtain full azimuth coverage. The use of a multitude of physical antenna units with fixed antenna lobes gives a static solution. If antenna elements are selected trough relays, some power will be lost in the switching arrangement. The use of relays implies more service and high outage time. Moreover, such an antenna arrangement will not allow elevation steering of the antenna lobe. As elevation can be very important if there are obstructions in the transmission path, this is clearly an inferior solution compared to a dynamic steering system that covers both azimuth and elevation.
US2004229652 discloses coordination of beam forming in wireless communication systems. US2004229652 especially relates to a method and system for coordinating the use of beam forming between two communicating entities in a wireless communication system. This publication is based on measuring the lobe pointing error and reducing it in steps until the pointing error is minimized. It is not disclosed, however, how the error initially is measured. Basically this publication is a simple approach to reducing a known pointing error. The system utilizes both omnidirectional and directive antennas and is therefore a complex solution.
US2011032149 discloses a system and method for antenna optimization for wireless broadband communication. The enhanced antenna array includes a higher-gain antenna and lower-gain antenna. The beam forming antenna, both higher-gain and lower-gain, are designed to be able to transmit to and receive from another transceiver. The higher-gain antenna is designed to form a more directional beam substantially closer to the horizon of an airborne platform; whereas the lower-gain antenna is designed to form a less directional beam at a distance further from the horizon of the airborne platform. Both the higher-gain and lower-gain antenna form their respective beams in the 360 degrees horizontally around the antenna array. The higher-gain antenna is designed for a coverage area from the horizon of the airborne platform to a substantially acute angle from the horizon of the airborne platform in the vertical direction and the lower-gain antenna is designed for a coverage area from the substantially acute angle from the horizon of the airborne platform to substantially vertical. The application of this publication is especially related to delivering data content over unlicensed radio frequency spectrum between airborne platform and surface base stations. Accordingly the system presumes that the airborne platforms communicates with base stations and is not arranged for communicating directly with each other which will be absolutely necessary in SIMOPS operations. The system is neither arranged for taking into consideration that communicating units will move during an operation, as the system is based on communicating with surface base stations which usually will have a fixed position. The system of US2011032149 uses the lower-gain antenna for searching for base stations and the higher-gain antenna for communicating with the base stations. As mentioned above the system of US2011032149 is not arranged for allowing users, i.e. airborne platforms to communicate directly with each other, but the users communicate with base stations which are connected in a network at their side to form a network via which base station network communication between units are possible. By having a higher-gain antenna and a lower-gain antenna results in that it requires two mechanical units and means for splitting the signal. Further, as mentioned above, the system of US2011032149 is not arranged for taking into consideration movement of other units, i.e. this will result in that if the unit the airborne platform is to communicate with is not within the coverage area of the lower-gain antenna, communication will not be possible. The same will also happen if the unit the airborne platform is to communicate with moves out of the coverage area of the lower-gain antenna, the communication will fail. This system is neither arranged for handling reflections, which will be present for maritime SIMOPS operations which will be discussed below.
Another problem that may arise when establishing maritime mobile networks is the local regime regarding allowed frequencies and power levels to be used. In maritime SIMOPS the field of operation may change globally and it is therefore necessary to adapt the use of frequencies and power levels to levels allowed in each geographical area. The national regulations regarding power levels and spectrum use may change substantially between different geographical locations and may have considerable differences between regions and countries. Moreover, in international waters the regulations will be different from national regulations. Based on this, power levels and frequencies may have to be changed from one area to another and even during a maritime SIMOPS operation if the area of operation encompasses more than one country or is partly in international waters.
Current systems rely on manual procedures to change frequencies and power levels when moving between areas with different jurisdiction. This may be a time consuming and cumbersome process that may lead to human errors when changing the required parameters.
Another problem that will arise in areas where there are a multitude of radio transmitters and radar systems is interference to the communication links. In a maritime SIMOPS operation, there will normally be a lot of radio transmitters operating on different frequencies. As most radio transmitters will have some harmonic and spurious radiation, the possibility of interference to a communication system is quite high.
Interference to the communication link can be very harmful and may even close down the communication link totally. Another severe case is when interference modifies data content in the data stream, thereby giving false data which under certain circumstances may lead to failure in the operation. The current procedure to avoid interference is often to manually change frequencies or power levels and thereby re-establishing a useful signal-to-noise-ratio. Depending on the interference source and the distance to the source, manual changes of parameters may or may not be successful.
A major problem regarding radio transmission over sea is reflections from the sea surface and attenuation and refraction of the signal in areas of high humidity. The received signal will be a sum of the direct signal and reflections from the sea surface and possibly other reflecting surface, such as vessel sides. Under adverse conditions these reflections may be of the same magnitude as the main signal and may therefore interfere severely with the main signal. As the phase of the reflected signal depends on the additional path length travelled and the reflection properties of the reflecting surface, the reflected signal may have the opposite phase of the direct signal and thereby cancelling it out.
During wind conditions the surface waves will change the position of the reflecting surface. This will introduce additional noise in the received signal and reduce the channel quality even more.
The current way of reducing the reflection from the sea surface is to use antennas with narrow lobes that suppress the unwanted signal as much as possible. Accordingly there exist no systems or methods which meet the special and demanding requirements set for maritime SIMOPS operations.
The main object of the disclosure is to provide a method and system which solves the above mentioned disadvantages with prior art related to maritime SIMOPS operations.
It is further an object of the disclosure to provide a method and system for providing a maritime high speed broadband communication network for SIMOPS operations.
An object of the disclosure is to provide a reliable, wireless long range, high speed data communication network for use in maritime SIMOPS operations.
Another object is to provide a method and a system which provides increased safety and security of an operation by introducing high speed data transmission from all sensors available.
It is further an object to provide a method and system which is less complex than prior art systems by using narrow phase steerable antennas being controllable in both azimuth and elevation by software control.
Another object of the disclosure is to provide a method and system providing actively monitoring of communication channels in use and arranged for using only free channels to avoid interference to other systems.
It is further an object of the disclosure to provide a method and system which is arranged to handle interference from reflecting signals by software control of the narrow phase steerable antenna, either at the receiving side, at the transmitting side or at both sides.
Another object of the disclosure is to provide a method and system which provides ranging between respective units.
It is further an object of the disclosure to provide a method and a system for actively compensating beam steering algorithms with regard to the movement of the unit carrying the phase steerable antenna.
Another object of the disclosure is to provide a method and a system arranged to use position data, like GPS data, to control operational parameters of the system, including position, heading and velocity of the unit carrying the phase steerable antenna.
It is further an object of the disclosure to provide a method and a system arranged for checking position data with positions obtained by measuring beam angels and time of flight of messages between two units.
Finally it is an object of the disclosure to provide a method and system for locally generating differential correction signals for GPS which can be used by any unit in the network.